1. Field of the Invention
The present invention relates to a control device for a vehicular drive system in which an output of a drive power source is transited to drive wheels of a vehicle through two transmission mechanisms, and more particularly to techniques for assuring high drivability of the vehicle when one of the two transmission mechanisms fails to be normally operable.
2 Discussion of the Related Art
There is known a vehicular drive system which includes two transmission mechanisms and in which an output of a drive power source is transmitted to drive wheels of a vehicle through the two transmission mechanisms. This vehicular drive system has an overall speed ratio determined by the speed ratios of the two transmission mechanisms.
Patent Document 1 discloses an example of a drive system for a hybrid vehicle, which is well known as a vehicular drive system including two transmission mechanisms as described above. The two transmission mechanisms provided in this vehicular drive system consist of an electrically controlled continuously variable transmission having a differential mechanism operable to distribute an output of an engine to a first electric motor and an output member, and a second electric motor disposed in a power transmitting path between the output member of the differential mechanism and the drive wheels of the vehicle, and a step-variable automatic transmission disposed in the power transmitting path. The electrically controlled continuously variable transmission is constituted by a planetary gear set, for example, and a major portion of a drive force of the engine is mechanically transmitted to the output member, through a differential function of the planetary gear set, while the remaining portion of the drive force of the engine is electrically transmitted from the first electric motor to the second electric motor through an electric path, whereby the speed ratio is electrically changed, so that the vehicle can be driven while the engine is held in an optimum operating state, with an improved fuel economy. The speed ratio of the step-variable automatic transmission permits the hybrid vehicle drive system to provide a vehicle drive force over a wide range of the overall speed ratio of the drive system, while minimizing the required size of the second electric motor.    [Patent Document 1] JP-2000-2327A    [Patent Document 2] JP-2000-346187A
Generally, a vehicular drive system is arranged such that in an abnormal or faulty state in which a transmission is not normally operable, the transmission is controlled to have a predetermined faulty-state speed ratio, to assure high drivability of the vehicle. This faulty-state speed ratio is selected to be relatively low for a relatively high output speed, for preventing an excessive engine braking effect during a high-speed running of the vehicle, and an excessively rise of an engine speed. Alternatively, the speed ratio established in the faulty state is selected to be relatively low for a relatively high output speed during the high-speed running of the vehicle, and to be relatively high for a relatively low output speed after an ignition switch is turned on, in order to obtain a sufficient vehicle drive force during starting of the vehicle or a low-speed running of the vehicle.
However, there is a possibility of deterioration of drivability of the vehicle due to a large difference of the faulty-state speed ratio with respect to the normal speed ratio established before detection of the faulty state, or due to a slow change of the speed ratio from the normal speed ratio to the faulty-state speed ratio upon detection of the faulty state. Where the drive system includes two transmission mechanisms as described above, there is also a possibility of deterioration of drivability of the vehicle in the faulty state of one of the two transmission mechanisms, in which the normally inoperable transmission is given a predetermined faulty-state speed ratio.
The present invention was made in view of the background situation described above. It is therefore an object of this invention to provide a control device for a vehicular drive system arranged to transmit an output of a drive power source to a drive wheel of a vehicle through two transmission mechanisms, which control device assures high drivability of the vehicle when one of the two transmission mechanisms fails to be normally operable.
The present invention defined in claim 1 provides a transmission portion and a second transmission portion and operable to transmit an output of a drive power source to a drive wheel of a vehicle through the first and second transmission portions, the control device comprising emergency transmission control means operable when one of the first and second transmission portions fails to be normally operable, the emergency transmission control means changing a speed ratio of the other of the first and second transmission portions.
In the above-described control device for a vehicular drive system including the first transmission portion and the second transmission portion, the emergency transmission control means is operated when one of the first and second transmission portions fails to be normally operable, so that the speed ratio of the other of the first and second transmission portions is changed by the emergency transmission control means. Accordingly, the emergency transmission control means reduces a change of the overall speed ratio of the drive system determined by the speed ratio of the first transmission portion and the speed ratio of the second transmission portion, thereby assuring high drivability of the vehicle. For example, the emergency transmission control means changes the speed ratio of the above-indicated other transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the above-indicated one transmission portion fails to be normally operable.
According to the present invention defined in claim 2, a speed ratio of the first transmission portion and a speed ratio of the second transmission portion determine an overall speed ratio of the vehicular drive system, and the emergency transmission control means changes the speed ratio of the above-indicated other transmission portion such that the overall speed ratio of the vehicular drive system changes toward a value immediate before the above-indicated one transmission portion fails to be normally operable. In this arrangement, a change of the overall speed ratio of the drive system is reduced, so that the vehicle can be run with high drivability. Where the speed ratio of the normally inoperable one of the two transmission portions changes to a value for a relatively high output speed, for example, the emergency transmission control portion increases the speed ratio of the other transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the above-indicated one transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an amount of reduction of a vehicle drive torque due to a change of the speed ratio of the normally inoperable transmission portion to the value for the relatively high output speed, thereby assuring high drivability of the vehicle. Where the speed ratio of the normally inoperable one of the two transmission portions changes to a value for a relatively low output speed, on the other hand, the emergency transmission control portion reduces the speed ratio of the other transmission portion such that the overall speed ratio of the drive system is made equal to the value immediately before the above-indicated one transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an engine braking effect generated due to a change of the speed ratio of the normally inoperable transmission portion to the value for the relatively low output speed, thereby assuring high drivability of the vehicle.
The present invention defined in claim 3 provides a control device for a vehicular drive system including a first transmission portion and a second transmission portion and operable to transmit an output of a drive power source to a drive wheel of a vehicle through the first and second transmission portions, the control device comprising emergency transmission control means operable when one of the first and second transmission portions fails to be normally operable, the emergency transmission control means placing the other of the first and second transmission portions in a neutral state in which a path of power transmission through the above-indicated other transmission portion is cut off.
In the above-described control device for a vehicular drive system including the first transmission portion and the second transmission portion, the emergency transmission control means is operated when one of the first and second transmission portions fails to be normally operable, so that the other of the first and second transmission portions is placed in its neutral state in which the path of power transmission through this other transmission portion is cut off. Accordingly, the emergency transmission control means prevents generation of an engine braking effect due to a change of the speed ratio of the normally inoperable transmission portion to a value for a relatively low output speed, or prevents an increase of the vehicle drive torque.
The present invention defined in claim 4 provides a control device for a vehicular drive system including a continuously-variable transmission portion operable as an electrically controlled continuously variable transmission and having a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, and further including a step-variable transmission portion which constitutes a part of the power transmitting path and which functions as a step-variable automatic transmission, the control device comprising emergency transmission control means operable when one of the continuously-variable and step-variable transmission portions fails to be normally operable, the emergency transmission control means changing a speed ratio of the other of the continuously-variable and step-variable transmission portions.
In the above-described control device for a vehicular drive system including the continuously-variable transmission portion and the step-variable transmission portion, the emergency transmission control means is operated when one of the continuously-variable and step-variable transmission portions fails to be normally operable, so that the speed ratio of the other of the continuously-variable and step-variable transmission portions is changed by the emergency transmission control means. Accordingly, the emergency transmission control means reduces a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion, thereby assuring high drivability of the vehicle. For example, the emergency transmission control means changes the speed ratio of the above-indicated other transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the above-indicated one transmission portion fails to be normally operable.
According to the present invention defined in claim 5, a speed ratio of the continuously-variable transmission portion and a speed ratio of the step-variable transmission portion determine an overall speed ratio of the vehicular drive system, and the emergency transmission control means changes the speed ratio of the above-indicated other transmission portion such that the overall speed ratio of the vehicular drive system changes toward a value immediate before the above-indicated one transmission portion fails to be normally operable. In this arrangement, a change of the overall speed ratio of the drive system is reduced, so that the vehicle can be run with high drivability. Where the speed ratio of the normally inoperable one of the two transmission portions changes to a value for a relatively high output speed, for example, the emergency transmission control portion increases the speed ratio of the other transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the above-indicated one transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an amount of reduction of a vehicle drive torque due to a change of the speed ratio of the normally inoperable transmission portion to the value for the relatively high output speed, thereby assuring high drivability of the vehicle. Where the speed ratio of the normally inoperable one of the two transmission portions changes to a value for a relatively low output speed, on the other hand, the emergency transmission control portion reduces the speed ratio of the other transmission portion such that the overall speed ratio of the drive system is made equal to the value immediately before the above-indicated one transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an engine braking effect generated due to a change of the speed ratio of the normally inoperable transmission portion to the value for the relatively low output speed, thereby assuring high drivability of the vehicle, or permits the drive system to provide a vehicle drive force over a wide range, by utilizing the speed ratio of the step-variable transmission portion, thereby increasing the operating efficiency of the electrically controlled continuously-variable transmission portion.
The present invention defined in claim 6 provides a control device for a vehicular drive system including a continuously-variable transmission portion operable as an electrically controlled continuously variable transmission and having a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, and further including a step-variable transmission portion which constitutes a part of the power transmitting path and which functions as a step-variable automatic transmission, the control device comprising emergency transmission control means operable when one of the continuously-variable and step-variable transmission portions fails to be normally operable, the emergency transmission control means placing the other of the continuously-variable and step-variable transmission portions in a neutral state in which a path of power transmission through the above-indicated other transmission portion is cut off.
In the above-described control device for a vehicular drive system including the continuously-variable transmission portion and the step-variable transmission portion, the emergency transmission control means is operated when one of the continuously-variable and step-variable transmission portions fails to be normally operable, so that the other of the continuously-variable and step-variable transmission portions is placed in its neutral state in which the path of power transmission through this above-indicated other transmission portion is cut off. Accordingly, the emergency transmission control means prevents generation of an engine braking effect due to a change of the speed ratio of the normally inoperable transmission portion to a value for a relatively low output speed, or prevents an increase of the vehicle drive torque.
The present invention defined in claim 7 provides a control device for a vehicular drive system including a continuously-variable transmission portion operable as an electrically controlled continuously variable transmission and having a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, and further including a step-variable transmission portion which constitutes a part of the power transmitting path and which functions as a step-variable automatic transmission, the control device comprising emergency transmission control means operable when the continuously-variable transmission portion fails to be normally operable, the emergency transmission control means changing a speed ratio of the step-variable transmission portion.
In the above-described control device for a vehicular drive system including the continuously-variable transmission portion and the step-variable transmission portion, the emergency transmission control means is operated when the continuously-variable transmission portion fails to be normally operable, so that the speed ratio of the step-variable transmission portion is changed by the emergency transmission control means. Accordingly, the emergency transmission control means reduces a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion, thereby assuring high drivability of the vehicle. For example, the emergency transmission control means changes the speed ratio of the step-variable transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the continuously-variable transmission portion fails to be normally operable.
According to the present invention defined in claim 8, the emergency transmission control means increases the speed ratio of the step-variable transmission portion when the continuously-variable transmission portion fails to be normally operable, with a result of a change of a speed ratio of the continuously-variable transmission portion to a value for a relatively high output speed. This arrangement is effective to reduce a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion. Where the speed ratio of the continuously-variable transmission portion changes to a value for a relatively high output speed, the emergency transmission control portion increases the speed ratio of the step-variable transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the continuously-variable transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an amount of reduction of the vehicle drive torque due to a change of the speed ratio of the normally inoperable transmission portion to the value for the relatively high output speed, thereby assuring high drivability of the vehicle.
According to the present invention defined in claim 9, the emergency transmission control means reduces the speed ratio of the step-variable transmission portion when the continuously-variable transmission portion fails to be normally operable, with a result of a change of a speed ratio of the continuously-variable transmission portion to a value for a relatively low output speed. This arrangement is effective to reduce a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion. Where the speed ratio of the continuously-variable transmission portion changes to a value for a relatively low output speed, the emergency transmission control portion reduces the speed ratio of the step-variable transmission portion such that the overall speed ratio of the drive system is made equal to the value immediately before the continuously-variable transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an engine braking effect generated due to a change of the speed ratio of the normally inoperable continuously-variable transmission portion to the value for the relatively low output speed, thereby assuring high drivability of the vehicle.
The present invention defined in claim 10 provides a control device for a vehicular drive system including a continuously-variable transmission portion operable as an electrically controlled continuously variable transmission and having a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, and further including a step-variable transmission portion which constitutes a part of the power transmitting path and which functions as a step-variable automatic transmission, said control device comprising emergency transmission control means operable when the continuously-variable transmission portion fails to be normally operable, the emergency transmission control means placing the step-variable transmission portion in a neutral state in which a path of power transmission through the step-variable transmission portion is cut off.
In the above-described control device for a vehicular drive system including the continuously-variable transmission portion and the step-variable transmission portion, the emergency transmission control means is operated when the continuously-variable transmission portion fails to be normally operable, so that the step-variable transmission portion is placed in its neutral state in which the path of power transmission through this step-variable transmission portion is cut off. Accordingly, the emergency transmission control means prevents generation of an engine braking effect due to a change of the speed ratio of the normally inoperable continuously-variable transmission portion to a value for a relatively low output speed, or prevents an increase of the vehicle drive torque.
The present invention defined in claim 11 provides a control device for a vehicular drive system including a continuously-variable transmission portion operable as an electrically controlled continuously variable transmission and having a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, and further including a step-variable transmission portion which constitutes a part of the power transmitting path and which functions as a step-variable automatic transmission, the control device comprising emergency transmission control means operable when the step-variable transmission portion fails to be normally operable, the emergency transmission control means changing a speed ratio of the continuously-variable transmission portion.
In the above-described control device for a vehicular drive system including the continuously-variable transmission portion and the step-variable transmission portion, the emergency transmission control means is operated when the step-variable transmission portion fails to be normally operable, so that the speed ratio of the continuously-variable transmission portion is changed by the emergency transmission control means. Accordingly, the emergency transmission control means reduces a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion, thereby assuring high drivability of the vehicle. For example, the emergency transmission control means changes the speed ratio of the continuously-variable transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the step-variable transmission portion fails to be normally operable.
According to the present invention defined in claim 12, the emergency transmission control means increases the speed ratio of the continuously-variable transmission portion when the step-variable transmission portion fails to be normally operable, with a result of a change of a speed ratio of the step-variable transmission portion to a value for a relatively high output speed. This arrangement is effective to reduce a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion. Where the speed ratio of the step-variable transmission portion changes to a value for a relatively high output speed, the emergency transmission control portion increases the speed ratio of the continuously-variable transmission portion such that the overall speed ratio of the drive system is made equal to a value immediately before the step-variable transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an amount of reduction of the vehicle drive torque due to a change of the speed ratio of the normally inoperable step-variable transmission portion to the value for the relatively high output speed, thereby assuring high drivability of the vehicle.
According to the present invention defined in claim 13, the emergency transmission control means reduces the speed ratio of the continuously-variable transmission portion when the step-variable transmission portion fails to be normally operable, with a result of a change of a speed ratio of the step-variable transmission portion to a value for a relatively low output speed. This arrangement is effective to reduce a change of the overall speed ratio of the drive system determined by the speed ratio of the continuously-variable transmission portion and the speed ratio of the step-variable transmission portion. Where the speed ratio of the step-variable transmission portion changes to a value for a relatively low output speed, the emergency transmission control portion reduces the speed ratio of the continuously-variable transmission portion such that the overall speed ratio of the drive system is made equal to the value immediately before the step-variable transmission portion fails to be normally operable. Accordingly, the emergency transmission control means reduces an engine braking effect generated due to a change of the speed ratio of the normally inoperable step-variable transmission portion to the value for the relatively low output speed, thereby assuring high drivability of the vehicle.
The present invention defined in claim 14 provides a control device for a vehicular drive system including a continuously-variable transmission portion operable as an electrically controlled continuously variable transmission and having a differential mechanism operable to distribute an output of an engine to a first electric motor and a power transmitting member, and a second electric motor disposed in a power transmitting path between the power transmitting member and a drive wheel of a vehicle, and further including a step-variable transmission portion which constitutes a part of the power transmitting path and which functions as a step-variable automatic transmission, said control device comprising emergency transmission control means operable when the step-variable transmission portion fails to be normally operable, the emergency transmission control means placing the continuously-variable transmission portion in a neutral state in which a path of power transmission through the continuously-variable transmission portion is cut off
In the above-described control device for a vehicular drive system including the continuously-variable transmission portion and the step-variable transmission portion, the emergency transmission control means is operated when the step-variable transmission portion fails to be normally operable, so that the continuously-variable transmission portion is placed in its neutral state in which the path of power transmission through this continuously-variable transmission portion is cut off. Accordingly, the emergency transmission control means prevents generation of an engine braking effect due to a change of the speed ratio of the normally inoperable step-variable transmission portion to a value for a relatively low output speed, or prevents an increase of the vehicle drive torque.
In a preferred form of the vehicular drive system according to any one of claims 4-14, the differential mechanism includes a differential-state switching device operable to place the differential mechanism selectively into a continuously-variable shifting state in which the continuously-variable transmission portion is operable as an electrically controlled continuously variable transmission, and a step-variable shifting state in which the continuously-variable transmission portion is not operable as the electrically controlled transmission. In this arrangement, the continuously-variable transmission portion can be easily switched between the continuously-variable shifting state and the step-variable shifting state.
Preferably, the differential-state switching device is operable to place the differential mechanism in a differential state in which the differential mechanism is operable to perform a differential function, whereby the continuously-variable transmission portion is placed in the continuously-variable shifting state, and to place the differential mechanism in a locked state in which the differential mechanism is not operable to perform the differential function, whereby the continuously-variable transmission portion is placed in the step-variable shifting state. Thus, the continuously-variable transmission portion is switchable between the continuously-variable shifting state and the step-variable shifting state.
Preferably, the differential mechanism includes a first element fixed to the engine, a second element fixed to the first electric motor, and a third element fixed to the power distributing member, and the above-indicated differential-state switching device is operable to permit the first, second and third elements to be rotated relative to each other, for thereby placing the differential mechanism in the continuously-variable shifting state, and to connect the first, second and third elements for rotation as a unit or to hold the second element stationary, for thereby placing the differential mechanism in the step-variable shifting state. In this arrangement, the continuously-variable transmission portion can be switched between the continuously-variable shifting state and the step-variable shifting state.
Preferably, the differential-state switching device includes a clutch operable to connect at least two of the first, second and third elements to each other for rotation of the first, second and third elements as a unit, and/or a brake operable to fix the second element to a stationary member for holding the second element stationary. In this arrangement, the continuously-variable transmission portion can be easily switched between the continuously-variable shifting state and the step-variable shifting state.
Preferably, the above-described clutch and the brake are released to place the differential mechanism is placed in the differential state in which the first, second and third elements are rotatable relative to each other. Further, the differential mechanism is enabled to function as a transmission having a speed ratio of 1 when the clutch is engaged, or as a speed-increasing transmission having a speed ratio lower than 1 when the brake is engaged. In this case, the differential mechanism can be switched between the differential state and the locked state, and can function as a transmission having one speed position with a fixed speed ratio or a plurality of speed positions with respective fixed speed ratios.
Preferably, the differential mechanism is a planetary gear set, and the above-described first, second and third elements are respectively a carrier, a sun gear and a ring gear of the planetary gear set. In this case, the required axial dimension of the differential mechanism can be reduced. Further, the differential mechanism can be simply constituted by one planetary gear set.
Preferably, the above-described planetary gear set is of a single-pinion type. In this case, the required axial dimension of the differential mechanism can be reduced. Further, the differential mechanism can be simply constituted by one planetary gear set of a single-pinion type.
In a preferred form of the present invention defined in any one of claims 7-14, the vehicular drive system has an overall speed ratio which is determined by the speed ratio of the step-variable transmission portion and the speed ratio of the continuously-variable transmission portion. In this case, the vehicular drive system provides a vehicle drive force over a wide range, by utilizing the speed ratio of the step-variable transmission portion, so that the continuously-variable transmission portion can be operated with increased operating efficiency as the electrically controlled transmission.